Counting circuitry employing multicathode glow transfer tube and a. c. bias source to increase circuit stability



July 27, 1965 C. B. FALCONER COUNTING GIRGUITRYv EMPLOYING MULTI-CATHODEGLOW TRANSFER TUBE AND A.C. BIAS SOURCE TO INCREASE CIRCUIT STABILITYFiled Oct. 4, 1962 D. c. VOLTAGE SOURCE l 1 u /4 E --1 R D FIG.

H% T? I FIG.2

INVENTOR CHARLES B. FALCONER BY WW,

ATTOR N EYS United States Patent C) V v p, 3,197,673 COUNTINGCIRCUI'I'RY EMPLOYING MULTL CATHODE GLOW TRANSFER AND A.-C. BIAS 'SOURGETO INCREASE CIRCUIT STABILITY Charles B. Falconer, Newton, Mass,'assi'g'n'or to Laboratory for Electronics, Inc., Boston, Mass, acorporation of Delaware 7 H Filed Oct. 4, 1962, Ser. No. 228,385 2Claims. (Cl. 315 84.6)

This invention relates in general to gas discharge tubes and inparticular to'a new and improved'technique for increasing thereliability and stability of counting circuits which include glowtransfer tubes.

Many of the commonly'used counting'circuits employ glow transfer tubesas their basic counting element. In such a tube, a glow discharge occursbetween -a central anode and one of several cathodes, usually ten, whichencircle the anode. By the application of a sequenceof pulses for eachcount, the discharge is transferred to the next adjacent cathode. Thecurrent surge arising from each such discharge flows through a cathoderesistor which must develop a voltage sufiicient to operate thefollowing circuits. If the voltage developed across the cathode resistoris to large, instabilities arise in the glow transfer tube and cause thedischarge to jump spuriously from one cathode to another. In a countingcircuit such transfer errors can be extremely serious. This problem isfelt most acutely in readout circuits which employ, in addition to theglow transfer tube, a series of individual gas discharge tubes, such asneon lamps, in the cathode circuits of the glow transfer tube toindicate the position of the count. An example of such a circuit may beseen in Patent No. 2,985,794, issued to E. R. Sarra'tt on May 23, 1961.

Although a bias is usually applied to place the neon lamps near theirmaintaining potential, the voltage developed across the cathode resistorof the 'glow discharge tube must still be sufii-ciently large to reachthe striking potential of the neon lamp in order to turn it on. At thesame time, this voltage must be kept sufiiciently low so thatinstabilities and spurious transfers do not occur in the glow transfertube. Since the D.C. bias of the neon lamps must be kept below theminimum maintaining potential and the voltage developed across theoathode resistor of the glow transfer tube plus the D.C. bias must reachthe maximum striking potential of all the neon lamps in the set, theneon lamps must be closely matched with each other so that the requiredvoltage swing may be minimized. While, in some cases, a matched set ofneon lamps may be obtained, which does allow the voltage swing to bekept within reasonable limits, such a set is extremely costly. Inaddition, there are usually six decades, that is, six glow transfertubes each with associated circuitry including a "series of neon lampsin a counting circuit, and hence the problem of matching each set toevery other set is encountered, thereby greatly increasing the rejectionrate and the overall cost.

It is, therefore, a primary object of the present invention to provide anew and improved technique whereby the signal voltage developed acrosseach cathode resistor in a glow transfer tube circuit utilizing neonlamps may be reduced, thereby eliminating the possibility of spurioustransfers.

It is another object of the present invention to reduce the necessaryD.C. voltage swing between the minimum maintaining potential and themaximum striking potential in a group of neon lamps, thereby resultingin a lower rejection rate.

It is a further object of the present invention to provide means forreducing the signal voltage necessary to operate a gas discharge tube.

Broadly speaking, the resent invention provides for the application'of acontinuous AC. voltage to'theiieon lamps in the readout circuit of aglew transfer tube. Under these conditions, the maximum ]).(3. voltageneeded to turn the neon lamps on is considerably lower and the minimumD.C. voltage 'Will "allow the neon lamps to turn off is now higher.Under these circumstances, the diiference between the two voltages, ie.the D.C. voltage signal which must be applied,- is reduced, with"consequent increase in circuit stability. Within ee'n tain limitations,this reduction may'beshovvn to be equal to the peak to peak value of theAC. voltage.-

These and other objects of the present invention to gether with furtherfeatures and advantages thereof 'will become more apparent from the-fellov'v'ing detailed description in which: M V q I FIG. '1diagrammaticany illustrates a typical embodiment of the presentinvention; and

FIG. 2 illustrates graphically the 'etfect'of theAQ. bias on thevoltages required to drive a gasdischa'rge tube.

In specific reference to FIG. 1, a glow transfer tube 10' is shownhaving therein an anode 12, a series of cathodes 14, and a series ofguides '16 and It? actuatedjby a ulse circuit '15. The anode 12 isconnected to a'eonstant high DE. voltage source 20 through the anoderesistor 21. The cathode resistors 22 are connected in parallel toground, While each of the cathodes 14 has a neon lamp 24 connectedthereto. All of the neon lamps 24 are connected in parallel to a D.C.bias source 26 which places them at a preselected potential. In additionto the D.C. bias source 26, an AC. voltage source 28 place'sjan;

A.C. voltage bias on each one of the neon lamps 24; the AC. source 28may be, for example; a sine wave generator which modulates the DI).bias.

The effect of the A.c. voltage source as 0a the Inagnn tude of the DC.voltages needed to rive the neon lamps 24 is shown in FIG. 2. ,Theminimum ni'ain'tfainingpotential for a group of rie'o i lamps isdesignated as e While the maximum maintaining potential is designated ase Similarly, the minimum striking potential is designated as e while themaximum striking potential is designated as e It is seen that forreliable neon operation, i.e. to ensure that all the neon lamps 24 willbe turned off and on, a D.C. voltage swing D is required which is equalto e.; (e d) where d is a voltage increment of sufiicient magnitudebelow the maintaining potential to extinguish the discharge. If,however, the applied D.C. drive voltages are modulated by an AC. voltagewith a peak to peak value of 2B, all the neon lamps 24 are turned offwhen the D.C. drive voltage is equal to (e d) +E) since on some portionof the negative half cycle of the AC. bias the drive voltage falls belowthe minimum maintaining potential 2 Such a minimum drive voltage isdesignated as 2 on the graph in FIG. 2;

the D.C. bias is, in practice, set at this level. Similarly,

all the neon lamps 24 are turned on by a drive voltage of e -E, since onsome portion of the positive half cycle of the AC. bias the drivevoltage is equal to the maxi mum striking potential. Such a maximumdrive voltage is designated as e It is seen, therefore, that the new required voltage swing D is equal to e -e which is equal Ifatented 'July27, 1965.

turned off during the negative half cycle of the AC. bias With drivevoltage e on, it is necessary that e 2E (or e E) be greater than e d.This imposes the limitation that 2E must be less than e -(e d). Theseconditions impose a maximum limitation on the peak to peak value of theAC. voltage. However, the DC. voltage swing required is still reduced bya significant factor. In a typical case, a voltage swing of 30 volts isreduced to 15 volts by use of the AC. bias with a peak to peak value of15 volts.

The AC. voltage in the present invention may merely be taken from a linecurrent of 60 c.p.s. Although all the neon'lamps may not strike (or turnoff) in succession at such a frequency, when the counting circuit isstopped to take a reading, the proper neon lamp will light in less than17 milliseconds (and any other improperly lit neon lamp will beextinguished). The fact that all the neon lamps do .not light (or turnoff) in succession is far overshadowed by the significant increaseobtained in stability and reliability of proper transfers in the glowtransfer tube. Moreover, the human eye does not tend to differentiatesuch a rapid succession of individual lamps if all were to lightconsecutively during the counting phase.

' While the use of the AC. biasing arrangement has been illustrated in acircuit for a glow transfer tube, nonetheless such a bias can be used inany circuit which requires that gas discharge tubes be turned on and or:with a minimum voltage swing. In addition, it is not necessary that aDC. bias voltage accompany this A.C. bias. Since, in this latter case,the gas discharge tubes are usually turned off by dropping the appliedvoltage to zero potential, the DC. voltage swing is reduced only by afactor of E. It should also be noted that the use of this technique neednot be restricted to gas discharge tubes; it can be applied to anynon-liner device which has a negative incremental resistance, AR,shortly after the initial rise of its operating curve; many such devicesare formed in the semiconductor field, such as tunnel diodes (where thevoltage changes discontinuously with small current changes) and certaintypes of transistors.

Having described the invention, it is apparent that numerousmodifications and improvements may be made by those skilled in the art,all of which fall within the scope of the invention; therefore, theinvention herein disclosed should be construed to be limited only by thespirit and scope of the appended claims.

What is claimed is:

1. An improved counting circuit in which a glow discharge issequentially transferred from one adjacent cathode to the next in a glowtransfer tube by a series of applied impulses comprising: a series ofgas discharge tubes each connected to one of said cathodes; means forsequentially applying a drive voltage to saidgas discharge tubes inresponse to said glow discharge; and means for applying a continuousA.C. voltage to each of said gas discharge tubes to reduce the magnitudeof the drive voltage necessary to reach the maximum striking potentialof said gas discharge tubes, said continuous AC. voltage having a peakto peak value less than twice the minimum striking potential of said gasdischarge tubes and not greater than the difference between the maximumstriking potential and the maximum maintaining potential.

2. An improved counting circuit in which a glow discharge issequentially transferred from one adjacent cathode to the next in a glowtransfer tube by a series of applied impulses comprising: a series ofgas discharge tubes each connected to one of said cathodes, said seriesbeing characterized by having a maximum and minimum striking potentialand a maximum and minimum maintaining potentiial; means for sequentiallyapplying a drive voltage to said gas discharge tubes in response to saidglow discharge; means for applying a D.C. bias to each of said gasdischarge tubes, said DC. bias having a preselected value not less thanthe minimum potential required to maintain a discharge in said gasdischarge tubes; and means for applying a continuous AC. voltage to eachof said gas discharge tubes, said continuous AC. voltage having a peakto peak value not greater than the difference between said minimumstriking potential and said minimum maintaining potential and notgreater than the difi'erence between said maximum striking potential andsaid maximum maintaining potential.

References Cited by the Examiner UNITED STATES PATENTS 2,920,239 1/60Saeger 3l5-l76 2,985,794 5/61 Sarratt 315-845 ARTHUR GAUSS, PrimaryExaminer.

1. AN IMPROVED COUNTING CIRCUIT IN WHICH A GLOW DISCHARGE ISSEQUENTIALLY TRANSFERRED FROM ONE ADJACENT CATHODE TO THE NEXT IN A GLOWTRANSFER TUBE BY A SERIES OF APPLIED IMPULSES COMPRISING: A SERIES OFGAS DISCHARGE TUBES EACH CONNECTED TO ONE OF SAID CATHODES; MEANS FORSEQUENTIALLY APPLYINGG A DRIVE VOLTAGE TO SAID GAS DISCHARGE TUBES INRESPONSE TO SAID GLOW DISCHARGE; AND MEANS FOR APPLYING A CONTINUOUSA.C. VOLTAGE TO EACH OF SAID GAS DISCHARGE TUBES TO REDUCE THE MAGNITUDEOF THE DRIVE VOLTAGE NECESSARY TO REACH THE MAXIMUM STRIKING POTENTIALOF SAID GAS DISCHARGE TUBES, SAID CONTINUOUS A.C. VOLTAGE HAVING A PEAKTO PEAK VALUE LESS THAN TWICE THE MINIMUM STRIKING POTENTIAL OF SAID GASDISCHARGE TUBES AND NOT GREATER THAN THE DIFFERENCE BETWEEN THE MAXIMUMSTRIKING POTENTIAL AND THE MAXIMUM MAINTAINING POTENTIAL.